12 Everyday Calculators in One Place: EMI, GST, BMI, Age and More (Free, No Sign-Up)

Every few days I catch myself doing the same thing: opening a search tab to find yet another single-purpose calculator site. One for a loan EMI, another for GST, a third for working out my exact age for a form.

Most of them are buried under pop-ups, some want an email address before showing a result, and all of them ask me to type personal numbers into a stranger's server. So I collected the twelve calculators I actually reach for and put them on one page of ToolNest, a small tools site I built.

Full disclosure, because this is DEV and you'd ask anyway: there is no backend doing this maths. Every calculator is plain JavaScript running in your browser tab. Nothing you type is uploaded, stored, or logged - close the tab and the numbers are gone. No account, no install, no "premium" tier.

Here they are, grouped the way I use them.

Loan EMI, with the maths shown

Before signing any loan - bike, phone, home, personal - it is worth knowing three numbers: the monthly instalment, the total interest, and the total amount you will actually hand over. The EMI Calculator gives all three from the loan amount, interest rate, and tenure.

It uses the standard reducing-balance formula:

EMI = P × r × (1 + r)^n / ((1 + r)^n − 1)

where r is the monthly rate (annual rate ÷ 12) and n is the number of months.

A worked example: borrow ₹5,00,000 at 9% for 5 years and you get:

• Monthly EMI: ₹10,379
• Total paid over 5 years: ₹6,22,751
• Total interest: ₹1,22,751

That last line is the one banks don't print in large type - the loan costs you roughly 25% on top of what you borrowed. Seeing it before you sign changes decisions.